Streptococcus pyogenes, group A Streptococcus, is a common human pathogen which causes a variety of diseases such as pharingitis, impetigo, scarlatina and erysipelas. More severe infections caused by this organism are necrotizing fasciitis and streptococcal toxic shock like syndrome.
The superfamily of ABC (ATP-binding cassette) transporters comprise many different systems in procaryotes and eukaryotes. This diverse group of transporters serve many roles including transport of nutrients, translocation of signal molecules and chemotaxis. The general principle of ABC transport includes transportation of a ligand through two integral membrane domains forming a pore, with accompanying ATP hydrolysis by two nucleotide-binding domains associated with the cytoplasmic side of the pore.
In bacteria, the translocation of ligands is preceded by interaction with an accessory component, the periplasmic binding protein. This protein binds the ligand with higher affinity, and then interacts with the integral membrane components by releasing the ligand and allowing subsequent transport. In gram-positive bacteria, the binding protein homologue is a lipoprotein attached to the cell membrane by a NH2-terminal lipid moiety. Little is known about the ABC transporters in gram-positive bacteria. In particular, the interaction between the lipid protein component and the integral membrane component is unclear.
A number of recent studies have looked at an ABC transporter family in Streptococcus species. Examples are Correia et al Infect. Immun (1996) 64(6) 2114-2121; Fenno et al Mol. Microbiol. (1995) 15(5) 849-863; Lowe et al Infect. Immun (1995) 63(2) 703-706; Kolenbrander et al Infect. Immun (1994) 62(10) 4469-4480 and Sampson et al Infect. Immun (1994) 62(1) 319-324.
The genes encoding the ABC transporter form an operon consisting of three genes. The putative proteins encoded by these genes are a hydrophobic membrane protein, a nucleotide binding protein and a lipid protein. The operon has been sequenced in a number of important disease causing organisms such as S.pneumoniae, Enterococcus faecalis, S.sanguis and S.parasanguis as well as in commensal bacteria such as S.gordonii and Streptococcus crista. As well as playing a role in transport, the ABC transporter has also been related to bacterial virulence and may mediate bacterial coaggregation, adhesion to host cells, saliva pellicle components and fibrin clots.